Early '08 20" 2.66GHz/HD2600 Pro startup issues

[mojolicious]

Have waded through a couple of years' worth of posts containing 'LED' without stumbling across anything relevant, but apologies if this has already been addressed.

I'm sprucing up a friend's ageing iMac with 4GB RAM, a fresh OS, etc etc. Obviously this involves multiple restarts, and the problem I've encountered is: it doesn't like restarts! There's power, there's (regular) fan noise, but no chime and no display.

Have cracked it open and only the first two LEDs light. Service Source for this model states "LED 3 indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement."

As I said, there's no startup sound. Is this a significant absence?

The 'cure' is to allow three or four minutes between restarts, ie let the iMac cool down. I'm assuming it's regular, beyond economic repair solder rot, but if anyone has any bright ideas I'd be glad to hear them.

(Luckily for me my friend has seen the problem for themselves in the past, so it's not something I've introduced; I guess restarts are vanishingly few and far between during regular day to day usage so they'd not viewed it as a 'problem')

 

[Brian33]

Hi -- my everyday machine is an Early 2008 iMac, but I have the 24" one (iMac 8,1) with the ATI Radeon HD 2600 Pro graphics card. The Service Manual for my machine says the same thing you posted above about the diagnostic LEDs.

One thought: for several years I had used my iMac with the "bong" startup sound disabled. I had come across a Terminal command to disable the startup sound. I believe it was a "defaults write" command, but unfortunately I no longer know the details. I initially set it when I was running 10.6 (Snow Leopard), and it continued to work for a year or two after I upgraded to 10.8 (Mountain Lion) with a DIY Fusion Drive. Unfortunately the "bong" has recently returned to my iMac and I'm not sure why...

Anyway, is it plausible that your friend could have disabled the startup sound similarly? If so (or if you could re-enable it), it would be a more clear indication of a video card fault.

Even if that's not the case, by guess is that the problem is indeed the video card. I haven't read much about the 20" model, but I've read plenty about video card problems with my 24" model, and it seems plausible to me that the startup chime presence/absence may not be significant. If you decide to pursue that hypothesis, you might consider "re-flowing" your video card. I haven't tried it myself, but I've read of others reporting success, using just a standard bake oven. (I'm assuming the graphics card in the 20" is removable, like it is in the 24" model.) However, my impression is that the re-flowing solution works for "awhile," but ultimately the card fails again.

Of course a better option would be if you could borrow an appropriate card from someone else and temporarily swap it in, but I'm sure you've already thought of that...

On a side note -- if the 20" is like my 24", you can put 6 GB of RAM in it (one 4 GB stick and one 2 GB stick) even though Apple says the max is 4 GB. I've had it that way for years -- check everymac.com for your model.

My 24" Early 2008 iMac is still going strong, and amazingly, I still like it! Hope you get your friend's working well, too!

 

[mojolicious]

Hi Brian, thanks for the reply.

My original post was unclear: when the iMac is feeling cooperative, there is the startup chime. It's only when it refuses to start that there's no sound, which isn't a scenario envisaged by Apple themselves ("If LEDs 1 and 2 are ON and you heard the startup sound..." etc etc). This is also following a reformat and OS (10.9) reinstall, so we can rule out use of a 'debonging' utility.

As you say, best guess is a video card problem. However I've not encountered any glitches, twitches or artifacts. The iMac's refusal to make warm restarts makes it a pain in the arse during installation, but much less so during normal usage. Furthermore it will wake from screen/disk sleep without any problems. It's almost as if the self-diagnostic on warm starts is returning a false fail.

Lifting the LCD panel to watch the LEDs is as far as I'm going with this one for the time being; if the video eventually fails then I might suggest trying a 'card bake' before binning the iMac, but I'm not going to do so preemptively.

The iMac has spent the last year in a cupboard, so who knows what knocks it's received. I suspect my friend has decided to resurrect the iMac only because she's recently taken out an Office 365 subscription for her newish MacBook Pro, and wants to get her money's worth by installing Office on as many devices as possible! 4GB of RAM should be fine, although an SSD would perk things up no end. I won't push it because a) having looked at the teardown it looks like a lot of eyestrain, and b) there's always the chance that the video card (or 'video card communication') is hanging on in there by an absolute thread, and disassembly to reach the the HDD will snap that thread.

 

[Brian33]

Ah, I see. It really does seem odd that you haven't had any "glitches, twitches or artifacts," yet have this warm restart issue. I don't recall reading about any similar case. I suppose a temp-induced failure on the graphics card could occur in only the circuits used during the POST boot-up process and not in the circuits used during "everyday" usage, but that sure stretches my imagination!

Wouldn't it be cool if you could have some sort of a remote temperature sensor placed near the graphics card with a readout on an independent device (i.e., not dependent upon the iMac) -- then you might be able say more definitely that the failure related to a specific temp range. I can't imagine what else it could be aside from a temp-related issue, but I guess I'm just curious and have a data-driven mindset. I have a cheap in/out weather temp device that would probably do the trick, but I guess it wouldn't really be worth the effort.

Yeah, I agree with you -- I wouldn't risk the crude card bake I suggested either, if it's working OK in normal use. Hopefully it won't get worse, but you might want to tell the owner to let you know if she starts seeing graphics anomalies.

It looks like we have the same graphics card. I had some such anomalies with my iMac back when I was on 10.6 (Snow Leopard). Oddly, my graphics issues corresponded to a subset of users whose graphics problems did not seem to be heat related. Instead, our issues were convincingly fixed by reverting to an older version of the ATI "drivers" (kext kernel extensions). After reverting the kexts, I never had graphics problems again, and somewhere along my OS X upgrade process I discovered that it was no longer necessary for me to manually change the drivers. So mine is OK (cross my fingers!).

I can understand not wanting to risk disassembly of these things! I approached it with great trepidation. (Although I'm pretty good with mechanical things like motorcycles and cars, I had almost no experience with the tiny fiddly bits and procedures needed for electronics.) However, with extreme care and patience following and ifixit guide, I was successful, and ultimately I decided it wasn't so hard after all. I replaced the original HDD with and SSD, and the optical drive with a 2.5" HDD, and set up my own DIY Fusion Drive. It's been wonderful! (Can you tell I'm proud of myself? Ha ha!)

Keep it in mind if the owner wants a nice "snappy" experience!

 

[almarzeta]

Yeah, I agree with you -- I wouldn't risk the crude card bake I suggested either, if it's working OK in normal use. Hopefully it won't get worse, but you might want to tell the owner to let you know if she starts seeing graphics anomalies.

It looks like we have the same graphics card. I had some such anomalies with my iMac back when I was on 10.6 (Snow Leopard). Oddly, my graphics issues corresponded to a subset of users whose graphics problems did not seem to be heat related. Instead, our issues were convincingly fixed by reverting to an older version of the ATI "drivers" (kext kernel extensions). After reverting the kexts, I never had graphics problems again, and somewhere along my OS X upgrade process I discovered that it was no longer necessary for me to manually change the drivers. So mine is OK (cross my fingers!).

Hi Brian! can you tell me how did you find out that the graphic card issue was not in fact heat related? im currently facing issues on my iMac 24'' mid 2007, it carries an ATI Radeon 2600 HD Pro 256MB and I can only start my iMac in safe mode. I would like to know how could you managed to fix this issues by reverting the ATI drivers, you see that the only fix possible besides replacing the video card I was about to do was baking the card as is the only way I can attemp that doesnt require changing the card itself.

 

[Brian33]

Hi -- I replied to you in the other thread:
https://forums.macrumors.com/threads/replacing-graphics-card-on-imac-8-1.1905172/